1. Field of the Invention
The present invention relates generally to timing systems and processes in computer systems, and more particularly, to a system and method for calibrating and setting a Time-of-Day (TOD) clock timing source.
2. Description of the Prior Art
In today's parallel sysplex, TOD clocks are externally synchronized through a special External Time Reference (ETR) console. However, in an STP only configuration, ETR connections will not be available. Also, ETR connections do not provide any detection mechanism for oscillator failures.
GPS receivers can also be used to synchronize system clocks. However, the IBM z-Series® e-Servers do not currently support GPS connections. Even if these server architectures supported GPS connections, there would still be needed a system to ensure the accuracy of the external time readings. GPS receivers do not provide the microsecond level of guaranteed accuracy that is available with the ETR connection. Additionally, the GPS mechanism provides no means for detecting oscillator failures.
It would be highly desirable to provide a system method for enabling a TOD clock to be synchronized to an external standard time source, such as Coordinated Universal Time (UTC), to an accuracy on the order of a microsecond, even in the presence of significant latency and jitter in the path that reads the current time value. For exemplary purposes, errors in the path referred to herein are on the order of +/−100 milliseconds. Second, it would further be highly desirable to provide a system and method that enables the TOD steering rate to be finely adjusted to overcome inherent errors in the crystal oscillator frequency. It would further be highly desirable to provide a system and method that enables the system to self-diagnose oscillator failures where the error in the oscillator frequency exceeds documented specifications for tolerable oscillator error. This condition results from the normal aging of oscillator crystals and is not currently detectable in a running server by any known mechanism.